update ios-tutorial to latest

done for [AGPUSH-850](https://issues.jboss.org/browse/AGPUSH-850)

the _Custom Keys_ section still references the CURL:
https://github.com/cvasilak/aerogear.org/blob/AGPUSH-850/docs/unifiedpush/aerogear-push-ios/send-push.asciidoc#custom-keys

Perhaps we keep the CURL, and explain that you are more flexible there ?